use crate::native_loader::NativeLoader;
use serde::{Deserialize, Serialize};
use solana_sdk::{
    account::{AccountSharedData, ReadableAccount, WritableAccount},
    account_utils::StateMut,
    bpf_loader_upgradeable::{self, UpgradeableLoaderState},
    ic_logger_msg, ic_msg,
    instruction::{CompiledInstruction, Instruction, InstructionError},
    keyed_account::{keyed_account_at_index, KeyedAccount},
    message::Message,
    process_instruction::{Executor, InvokeContext, Logger, ProcessInstructionWithContext},
    pubkey::Pubkey,
    rent::Rent,
    system_program,
};
use std::{
    cell::{Ref, RefCell},
    collections::HashMap,
    rc::Rc,
    sync::Arc,
};

pub struct Executors {
    pub executors: HashMap<Pubkey, Arc<dyn Executor>>,
    pub is_dirty: bool,
}
impl Default for Executors {
    fn default() -> Self {
        Self {
            executors: HashMap::default(),
            is_dirty: false,
        }
    }
}
impl Executors {
    pub fn insert(&mut self, key: Pubkey, executor: Arc<dyn Executor>) {
        let _ = self.executors.insert(key, executor);
        self.is_dirty = true;
    }
    pub fn get(&self, key: &Pubkey) -> Option<Arc<dyn Executor>> {
        self.executors.get(key).cloned()
    }
}

#[derive(Default, Debug)]
pub struct ProgramTiming {
    pub accumulated_us: u64,
    pub accumulated_units: u64,
    pub count: u32,
}

#[derive(Default, Debug)]
pub struct ExecuteDetailsTimings {
    pub serialize_us: u64,
    pub create_vm_us: u64,
    pub execute_us: u64,
    pub deserialize_us: u64,
    pub changed_account_count: u64,
    pub total_account_count: u64,
    pub total_data_size: usize,
    pub data_size_changed: usize,
    pub per_program_timings: HashMap<Pubkey, ProgramTiming>,
}
impl ExecuteDetailsTimings {
    pub fn accumulate(&mut self, other: &ExecuteDetailsTimings) {
        self.serialize_us += other.serialize_us;
        self.create_vm_us += other.create_vm_us;
        self.execute_us += other.execute_us;
        self.deserialize_us += other.deserialize_us;
        self.changed_account_count += other.changed_account_count;
        self.total_account_count += other.total_account_count;
        self.total_data_size += other.total_data_size;
        self.data_size_changed += other.data_size_changed;
        for (id, other) in &other.per_program_timings {
            let program_timing = self.per_program_timings.entry(*id).or_default();
            program_timing.accumulated_us = program_timing
                .accumulated_us
                .saturating_add(other.accumulated_us);
            program_timing.accumulated_units = program_timing
                .accumulated_units
                .saturating_add(other.accumulated_units);
            program_timing.count = program_timing.count.saturating_add(other.count);
        }
    }
    pub fn accumulate_program(&mut self, program_id: &Pubkey, us: u64, units: u64) {
        let program_timing = self.per_program_timings.entry(*program_id).or_default();
        program_timing.accumulated_us = program_timing.accumulated_us.saturating_add(us);
        program_timing.accumulated_units = program_timing.accumulated_units.saturating_add(units);
        program_timing.count = program_timing.count.saturating_add(1);
    }
}

// The relevant state of an account before an Instruction executes, used
// to verify account integrity after the Instruction completes
#[derive(Clone, Debug, Default)]
pub struct PreAccount {
    key: Pubkey,
    account: Rc<RefCell<AccountSharedData>>,
    changed: bool,
}
impl PreAccount {
    pub fn new(key: &Pubkey, account: &AccountSharedData) -> Self {
        Self {
            key: *key,
            account: Rc::new(RefCell::new(account.clone())),
            changed: false,
        }
    }

    pub fn verify(
        &self,
        program_id: &Pubkey,
        is_writable: bool,
        rent: &Rent,
        post: &AccountSharedData,
        timings: &mut ExecuteDetailsTimings,
        outermost_call: bool,
        updated_verify_policy: bool,
    ) -> Result<(), InstructionError> {
        let pre = self.account.borrow();

        // Only the owner of the account may change owner and
        //   only if the account is writable and
        //   only if the account is not executable and
        //   only if the data is zero-initialized or empty
        let owner_changed = pre.owner() != post.owner();
        if owner_changed
            && (!is_writable // line coverage used to get branch coverage
                || pre.executable()
                || program_id != pre.owner()
            || !Self::is_zeroed(post.data()))
        {
            return Err(InstructionError::ModifiedProgramId);
        }

        // An account not assigned to the program cannot have its balance decrease.
        if program_id != pre.owner() // line coverage used to get branch coverage
         && pre.lamports() > post.lamports()
        {
            return Err(InstructionError::ExternalAccountLamportSpend);
        }

        // The balance of read-only and executable accounts may not change
        let lamports_changed = pre.lamports() != post.lamports();
        if lamports_changed {
            if !is_writable {
                return Err(InstructionError::ReadonlyLamportChange);
            }
            if pre.executable() {
                return Err(InstructionError::ExecutableLamportChange);
            }
        }

        // Only the system program can change the size of the data
        //  and only if the system program owns the account
        let data_len_changed = pre.data().len() != post.data().len();
        if data_len_changed
            && (!system_program::check_id(program_id) // line coverage used to get branch coverage
                || !system_program::check_id(pre.owner()))
        {
            return Err(InstructionError::AccountDataSizeChanged);
        }

        // Only the owner may change account data
        //   and if the account is writable
        //   and if the account is not executable
        if !(program_id == pre.owner()
            && is_writable  // line coverage used to get branch coverage
            && !pre.executable())
            && pre.data() != post.data()
        {
            if pre.executable() {
                return Err(InstructionError::ExecutableDataModified);
            } else if is_writable {
                return Err(InstructionError::ExternalAccountDataModified);
            } else {
                return Err(InstructionError::ReadonlyDataModified);
            }
        }

        // executable is one-way (false->true) and only the account owner may set it.
        let executable_changed = pre.executable() != post.executable();
        if executable_changed {
            if !rent.is_exempt(post.lamports(), post.data().len()) {
                return Err(InstructionError::ExecutableAccountNotRentExempt);
            }
            let owner = if updated_verify_policy {
                post.owner()
            } else {
                pre.owner()
            };
            if !is_writable // line coverage used to get branch coverage
                || pre.executable()
                || program_id != owner
            {
                return Err(InstructionError::ExecutableModified);
            }
        }

        // No one modifies rent_epoch (yet).
        let rent_epoch_changed = pre.rent_epoch() != post.rent_epoch();
        if rent_epoch_changed {
            return Err(InstructionError::RentEpochModified);
        }

        if outermost_call {
            timings.total_account_count += 1;
            timings.total_data_size += post.data().len();
            if owner_changed
                || lamports_changed
                || data_len_changed
                || executable_changed
                || rent_epoch_changed
                || self.changed
            {
                timings.changed_account_count += 1;
                timings.data_size_changed += post.data().len();
            }
        }

        Ok(())
    }

    pub fn update(&mut self, account: &AccountSharedData) {
        let mut pre = self.account.borrow_mut();
        let rent_epoch = pre.rent_epoch();
        *pre = account.clone();
        pre.set_rent_epoch(rent_epoch);

        self.changed = true;
    }

    pub fn key(&self) -> &Pubkey {
        &self.key
    }

    pub fn data(&self) -> Ref<[u8]> {
        Ref::map(self.account.borrow(), |account| account.data())
    }

    pub fn lamports(&self) -> u64 {
        self.account.borrow().lamports()
    }

    pub fn executable(&self) -> bool {
        self.account.borrow().executable()
    }

    pub fn is_zeroed(buf: &[u8]) -> bool {
        const ZEROS_LEN: usize = 1024;
        static ZEROS: [u8; ZEROS_LEN] = [0; ZEROS_LEN];
        let mut chunks = buf.chunks_exact(ZEROS_LEN);

        chunks.all(|chunk| chunk == &ZEROS[..])
            && chunks.remainder() == &ZEROS[..chunks.remainder().len()]
    }
}

#[derive(Deserialize, Serialize)]
pub struct InstructionProcessor {
    #[serde(skip)]
    programs: Vec<(Pubkey, ProcessInstructionWithContext)>,
    #[serde(skip)]
    native_loader: NativeLoader,
}

impl std::fmt::Debug for InstructionProcessor {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        #[derive(Debug)]
        struct MessageProcessor<'a> {
            programs: Vec<String>,
            native_loader: &'a NativeLoader,
        }

        // These are just type aliases for work around of Debug-ing above pointers
        type ErasedProcessInstructionWithContext = fn(
            &'static Pubkey,
            &'static [u8],
            &'static mut dyn InvokeContext,
        ) -> Result<(), InstructionError>;

        // rustc doesn't compile due to bug without this work around
        // https://github.com/rust-lang/rust/issues/50280
        // https://users.rust-lang.org/t/display-function-pointer/17073/2
        let processor = MessageProcessor {
            programs: self
                .programs
                .iter()
                .map(|(pubkey, instruction)| {
                    let erased_instruction: ErasedProcessInstructionWithContext = *instruction;
                    format!("{}: {:p}", pubkey, erased_instruction)
                })
                .collect::<Vec<_>>(),
            native_loader: &self.native_loader,
        };

        write!(f, "{:?}", processor)
    }
}

impl Default for InstructionProcessor {
    fn default() -> Self {
        Self {
            programs: vec![],
            native_loader: NativeLoader::default(),
        }
    }
}
impl Clone for InstructionProcessor {
    fn clone(&self) -> Self {
        InstructionProcessor {
            programs: self.programs.clone(),
            native_loader: NativeLoader::default(),
        }
    }
}

#[cfg(RUSTC_WITH_SPECIALIZATION)]
impl ::solana_frozen_abi::abi_example::AbiExample for InstructionProcessor {
    fn example() -> Self {
        // MessageProcessor's fields are #[serde(skip)]-ed and not Serialize
        // so, just rely on Default anyway.
        InstructionProcessor::default()
    }
}

impl InstructionProcessor {
    pub fn programs(&self) -> &[(Pubkey, ProcessInstructionWithContext)] {
        &self.programs
    }

    /// Add a static entrypoint to intercept instructions before the dynamic loader.
    pub fn add_program(
        &mut self,
        program_id: Pubkey,
        process_instruction: ProcessInstructionWithContext,
    ) {
        match self.programs.iter_mut().find(|(key, _)| program_id == *key) {
            Some((_, processor)) => *processor = process_instruction,
            None => self.programs.push((program_id, process_instruction)),
        }
    }

    /// Create the KeyedAccounts that will be passed to the program
    pub fn create_keyed_accounts<'a>(
        message: &'a Message,
        instruction: &'a CompiledInstruction,
        executable_accounts: &'a [(Pubkey, Rc<RefCell<AccountSharedData>>)],
        accounts: &'a [(Pubkey, Rc<RefCell<AccountSharedData>>)],
    ) -> Vec<(bool, bool, &'a Pubkey, &'a RefCell<AccountSharedData>)> {
        executable_accounts
            .iter()
            .map(|(key, account)| (false, false, key, account as &RefCell<AccountSharedData>))
            .chain(instruction.accounts.iter().map(|index| {
                let index = *index as usize;
                (
                    message.is_signer(index),
                    message.is_writable(index),
                    &accounts[index].0,
                    &accounts[index].1 as &RefCell<AccountSharedData>,
                )
            }))
            .collect::<Vec<_>>()
    }

    /// Process an instruction
    /// This method calls the instruction's program entrypoint method
    pub fn process_instruction(
        &self,
        program_id: &Pubkey,
        instruction_data: &[u8],
        invoke_context: &mut dyn InvokeContext,
    ) -> Result<(), InstructionError> {
        if let Some(root_account) = invoke_context.get_keyed_accounts()?.iter().next() {
            let root_id = root_account.unsigned_key();
            if solana_sdk::native_loader::check_id(&root_account.owner()?) {
                for (id, process_instruction) in &self.programs {
                    if id == root_id {
                        invoke_context.remove_first_keyed_account()?;
                        // Call the builtin program
                        return process_instruction(program_id, instruction_data, invoke_context);
                    }
                }
                // Call the program via the native loader
                return self.native_loader.process_instruction(
                    &solana_sdk::native_loader::id(),
                    instruction_data,
                    invoke_context,
                );
            } else {
                let owner_id = &root_account.owner()?;
                for (id, process_instruction) in &self.programs {
                    if id == owner_id {
                        // Call the program via a builtin loader
                        return process_instruction(program_id, instruction_data, invoke_context);
                    }
                }
            }
        }
        Err(InstructionError::UnsupportedProgramId)
    }

    pub fn create_message(
        instruction: &Instruction,
        keyed_accounts: &[&KeyedAccount],
        signers: &[Pubkey],
        invoke_context: &Ref<&mut dyn InvokeContext>,
    ) -> Result<(Message, Pubkey, usize), InstructionError> {
        // Check for privilege escalation
        for account in instruction.accounts.iter() {
            let keyed_account = keyed_accounts
                .iter()
                .find_map(|keyed_account| {
                    if &account.pubkey == keyed_account.unsigned_key() {
                        Some(keyed_account)
                    } else {
                        None
                    }
                })
                .ok_or_else(|| {
                    ic_msg!(
                        invoke_context,
                        "Instruction references an unknown account {}",
                        account.pubkey
                    );
                    InstructionError::MissingAccount
                })?;
            // Readonly account cannot become writable
            if account.is_writable && !keyed_account.is_writable() {
                ic_msg!(
                    invoke_context,
                    "{}'s writable privilege escalated",
                    account.pubkey
                );
                return Err(InstructionError::PrivilegeEscalation);
            }

            if account.is_signer && // If message indicates account is signed
            !( // one of the following needs to be true:
                keyed_account.signer_key().is_some() // Signed in the parent instruction
                || signers.contains(&account.pubkey) // Signed by the program
            ) {
                ic_msg!(
                    invoke_context,
                    "{}'s signer privilege escalated",
                    account.pubkey
                );
                return Err(InstructionError::PrivilegeEscalation);
            }
        }

        // validate the caller has access to the program account and that it is executable
        let program_id = instruction.program_id;
        match keyed_accounts
            .iter()
            .find(|keyed_account| &program_id == keyed_account.unsigned_key())
        {
            Some(keyed_account) => {
                if !keyed_account.executable()? {
                    ic_msg!(
                        invoke_context,
                        "Account {} is not executable",
                        keyed_account.unsigned_key()
                    );
                    return Err(InstructionError::AccountNotExecutable);
                }
            }
            None => {
                ic_msg!(invoke_context, "Unknown program {}", program_id);
                return Err(InstructionError::MissingAccount);
            }
        }

        let message = Message::new(&[instruction.clone()], None);
        let program_id_index = message.instructions[0].program_id_index as usize;

        Ok((message, program_id, program_id_index))
    }

    /// Entrypoint for a cross-program invocation from a native program
    pub fn native_invoke(
        invoke_context: &mut dyn InvokeContext,
        instruction: Instruction,
        keyed_account_indices: &[usize],
        signers: &[Pubkey],
    ) -> Result<(), InstructionError> {
        let invoke_context = RefCell::new(invoke_context);

        let (
            message,
            executable_accounts,
            accounts,
            keyed_account_indices_reordered,
            caller_write_privileges,
        ) = {
            let invoke_context = invoke_context.borrow();

            // Translate and verify caller's data
            let keyed_accounts = invoke_context.get_keyed_accounts()?;
            let keyed_accounts = keyed_account_indices
                .iter()
                .map(|index| keyed_account_at_index(keyed_accounts, *index))
                .collect::<Result<Vec<&KeyedAccount>, InstructionError>>()?;
            let (message, callee_program_id, _) =
                Self::create_message(&instruction, &keyed_accounts, signers, &invoke_context)?;
            let keyed_accounts = invoke_context.get_keyed_accounts()?;
            let mut caller_write_privileges = keyed_account_indices
                .iter()
                .map(|index| keyed_accounts[*index].is_writable())
                .collect::<Vec<bool>>();
            caller_write_privileges.insert(0, false);
            let mut accounts = vec![];
            let mut keyed_account_indices_reordered = vec![];
            let keyed_accounts = invoke_context.get_keyed_accounts()?;
            'root: for account_key in message.account_keys.iter() {
                for keyed_account_index in keyed_account_indices {
                    let keyed_account = &keyed_accounts[*keyed_account_index];
                    if account_key == keyed_account.unsigned_key() {
                        accounts.push((*account_key, Rc::new(keyed_account.account.clone())));
                        keyed_account_indices_reordered.push(*keyed_account_index);
                        continue 'root;
                    }
                }
                ic_msg!(
                    invoke_context,
                    "Instruction references an unknown account {}",
                    account_key
                );
                return Err(InstructionError::MissingAccount);
            }

            // Process instruction

            invoke_context.record_instruction(&instruction);

            let program_account =
                invoke_context
                    .get_account(&callee_program_id)
                    .ok_or_else(|| {
                        ic_msg!(invoke_context, "Unknown program {}", callee_program_id);
                        InstructionError::MissingAccount
                    })?;
            if !program_account.borrow().executable() {
                ic_msg!(
                    invoke_context,
                    "Account {} is not executable",
                    callee_program_id
                );
                return Err(InstructionError::AccountNotExecutable);
            }
            let programdata = if program_account.borrow().owner() == &bpf_loader_upgradeable::id() {
                if let UpgradeableLoaderState::Program {
                    programdata_address,
                } = program_account.borrow().state()?
                {
                    if let Some(account) = invoke_context.get_account(&programdata_address) {
                        Some((programdata_address, account))
                    } else {
                        ic_msg!(
                            invoke_context,
                            "Unknown upgradeable programdata account {}",
                            programdata_address,
                        );
                        return Err(InstructionError::MissingAccount);
                    }
                } else {
                    ic_msg!(
                        invoke_context,
                        "Upgradeable program account state not valid {}",
                        callee_program_id,
                    );
                    return Err(InstructionError::MissingAccount);
                }
            } else {
                None
            };
            let mut executable_accounts = vec![(callee_program_id, program_account)];
            if let Some(programdata) = programdata {
                executable_accounts.push(programdata);
            }
            (
                message,
                executable_accounts,
                accounts,
                keyed_account_indices_reordered,
                caller_write_privileges,
            )
        };

        #[allow(clippy::deref_addrof)]
        InstructionProcessor::process_cross_program_instruction(
            &message,
            &executable_accounts,
            &accounts,
            &caller_write_privileges,
            *(&mut *(invoke_context.borrow_mut())),
        )?;

        // Copy results back to caller

        {
            let invoke_context = invoke_context.borrow();
            let keyed_accounts = invoke_context.get_keyed_accounts()?;
            for (src_keyed_account_index, ((_key, account), dst_keyed_account_index)) in accounts
                .iter()
                .zip(keyed_account_indices_reordered)
                .enumerate()
            {
                let dst_keyed_account = &keyed_accounts[dst_keyed_account_index];
                let src_keyed_account = account.borrow();
                if message.is_writable(src_keyed_account_index) && !src_keyed_account.executable() {
                    if dst_keyed_account.data_len()? != src_keyed_account.data().len()
                        && dst_keyed_account.data_len()? != 0
                    {
                        // Only support for `CreateAccount` at this time.
                        // Need a way to limit total realloc size across multiple CPI calls
                        ic_msg!(
                            invoke_context,
                            "Inner instructions do not support realloc, only SystemProgram::CreateAccount",
                        );
                        return Err(InstructionError::InvalidRealloc);
                    }
                    dst_keyed_account
                        .try_account_ref_mut()?
                        .set_lamports(src_keyed_account.lamports());
                    dst_keyed_account
                        .try_account_ref_mut()?
                        .set_owner(*src_keyed_account.owner());
                    dst_keyed_account
                        .try_account_ref_mut()?
                        .set_data(src_keyed_account.data().to_vec());
                }
            }
        }

        Ok(())
    }

    /// Process a cross-program instruction
    /// This method calls the instruction's program entrypoint function
    pub fn process_cross_program_instruction(
        message: &Message,
        executable_accounts: &[(Pubkey, Rc<RefCell<AccountSharedData>>)],
        accounts: &[(Pubkey, Rc<RefCell<AccountSharedData>>)],
        caller_write_privileges: &[bool],
        invoke_context: &mut dyn InvokeContext,
    ) -> Result<(), InstructionError> {
        if let Some(instruction) = message.instructions.get(0) {
            let program_id = instruction.program_id(&message.account_keys);

            // Verify the calling program hasn't misbehaved
            invoke_context.verify_and_update(instruction, accounts, caller_write_privileges)?;

            // Construct keyed accounts
            let keyed_accounts =
                Self::create_keyed_accounts(message, instruction, executable_accounts, accounts);

            // Invoke callee
            invoke_context.push(program_id, &keyed_accounts)?;

            let mut instruction_processor = InstructionProcessor::default();
            for (program_id, process_instruction) in invoke_context.get_programs().iter() {
                instruction_processor.add_program(*program_id, *process_instruction);
            }

            let mut result = instruction_processor.process_instruction(
                program_id,
                &instruction.data,
                invoke_context,
            );
            if result.is_ok() {
                // Verify the called program has not misbehaved
                let write_privileges: Vec<bool> = (0..message.account_keys.len())
                    .map(|i| message.is_writable(i))
                    .collect();
                result = invoke_context.verify_and_update(instruction, accounts, &write_privileges);
            }

            // Restore previous state
            invoke_context.pop();
            result
        } else {
            // This function is always called with a valid instruction, if that changes return an error
            Err(InstructionError::GenericError)
        }
    }

    /// Record the initial state of the accounts so that they can be compared
    /// after the instruction is processed
    pub fn create_pre_accounts(
        message: &Message,
        instruction: &CompiledInstruction,
        accounts: &[(Pubkey, Rc<RefCell<AccountSharedData>>)],
    ) -> Vec<PreAccount> {
        let mut pre_accounts = Vec::with_capacity(instruction.accounts.len());
        {
            let mut work = |_unique_index: usize, account_index: usize| {
                if account_index < message.account_keys.len() && account_index < accounts.len() {
                    let account = accounts[account_index].1.borrow();
                    pre_accounts.push(PreAccount::new(&accounts[account_index].0, &account));
                    return Ok(());
                }
                Err(InstructionError::MissingAccount)
            };
            let _ = instruction.visit_each_account(&mut work);
        }
        pre_accounts
    }

    /// Verify the results of a cross-program instruction
    #[allow(clippy::too_many_arguments)]
    pub fn verify_and_update(
        instruction: &CompiledInstruction,
        pre_accounts: &mut [PreAccount],
        accounts: &[(Pubkey, Rc<RefCell<AccountSharedData>>)],
        program_id: &Pubkey,
        rent: &Rent,
        write_privileges: &[bool],
        timings: &mut ExecuteDetailsTimings,
        logger: Rc<RefCell<dyn Logger>>,
        updated_verify_policy: bool,
    ) -> Result<(), InstructionError> {
        // Verify the per-account instruction results
        let (mut pre_sum, mut post_sum) = (0_u128, 0_u128);
        let mut work = |_unique_index: usize, account_index: usize| {
            if account_index < write_privileges.len() && account_index < accounts.len() {
                let (key, account) = &accounts[account_index];
                let is_writable = write_privileges[account_index];
                // Find the matching PreAccount
                for pre_account in pre_accounts.iter_mut() {
                    if key == pre_account.key() {
                        {
                            // Verify account has no outstanding references
                            let _ = account
                                .try_borrow_mut()
                                .map_err(|_| InstructionError::AccountBorrowOutstanding)?;
                        }
                        let account = account.borrow();
                        pre_account
                            .verify(
                                program_id,
                                is_writable,
                                rent,
                                &account,
                                timings,
                                false,
                                updated_verify_policy,
                            )
                            .map_err(|err| {
                                ic_logger_msg!(logger, "failed to verify account {}: {}", key, err);
                                err
                            })?;
                        pre_sum += u128::from(pre_account.lamports());
                        post_sum += u128::from(account.lamports());
                        if is_writable && !pre_account.executable() {
                            pre_account.update(&account);
                        }
                        return Ok(());
                    }
                }
            }
            Err(InstructionError::MissingAccount)
        };
        instruction.visit_each_account(&mut work)?;

        // Verify that the total sum of all the lamports did not change
        if pre_sum != post_sum {
            return Err(InstructionError::UnbalancedInstruction);
        }
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use solana_sdk::{account::Account, instruction::InstructionError};

    #[test]
    fn test_is_zeroed() {
        const ZEROS_LEN: usize = 1024;
        let mut buf = [0; ZEROS_LEN];
        assert!(PreAccount::is_zeroed(&buf));
        buf[0] = 1;
        assert!(!PreAccount::is_zeroed(&buf));

        let mut buf = [0; ZEROS_LEN - 1];
        assert!(PreAccount::is_zeroed(&buf));
        buf[0] = 1;
        assert!(!PreAccount::is_zeroed(&buf));

        let mut buf = [0; ZEROS_LEN + 1];
        assert!(PreAccount::is_zeroed(&buf));
        buf[0] = 1;
        assert!(!PreAccount::is_zeroed(&buf));

        let buf = vec![];
        assert!(PreAccount::is_zeroed(&buf));
    }

    struct Change {
        program_id: Pubkey,
        is_writable: bool,
        rent: Rent,
        pre: PreAccount,
        post: AccountSharedData,
    }
    impl Change {
        pub fn new(owner: &Pubkey, program_id: &Pubkey) -> Self {
            Self {
                program_id: *program_id,
                rent: Rent::default(),
                is_writable: true,
                pre: PreAccount::new(
                    &solana_sdk::pubkey::new_rand(),
                    &AccountSharedData::from(Account {
                        owner: *owner,
                        lamports: std::u64::MAX,
                        data: vec![],
                        ..Account::default()
                    }),
                ),
                post: AccountSharedData::from(Account {
                    owner: *owner,
                    lamports: std::u64::MAX,
                    ..Account::default()
                }),
            }
        }
        pub fn read_only(mut self) -> Self {
            self.is_writable = false;
            self
        }
        pub fn executable(mut self, pre: bool, post: bool) -> Self {
            self.pre.account.borrow_mut().set_executable(pre);
            self.post.set_executable(post);
            self
        }
        pub fn lamports(mut self, pre: u64, post: u64) -> Self {
            self.pre.account.borrow_mut().set_lamports(pre);
            self.post.set_lamports(post);
            self
        }
        pub fn owner(mut self, post: &Pubkey) -> Self {
            self.post.set_owner(*post);
            self
        }
        pub fn data(mut self, pre: Vec<u8>, post: Vec<u8>) -> Self {
            self.pre.account.borrow_mut().set_data(pre);
            self.post.set_data(post);
            self
        }
        pub fn rent_epoch(mut self, pre: u64, post: u64) -> Self {
            self.pre.account.borrow_mut().set_rent_epoch(pre);
            self.post.set_rent_epoch(post);
            self
        }
        pub fn verify(&self) -> Result<(), InstructionError> {
            self.pre.verify(
                &self.program_id,
                self.is_writable,
                &self.rent,
                &self.post,
                &mut ExecuteDetailsTimings::default(),
                false,
                true,
            )
        }
    }

    #[test]
    fn test_verify_account_changes_owner() {
        let system_program_id = system_program::id();
        let alice_program_id = solana_sdk::pubkey::new_rand();
        let mallory_program_id = solana_sdk::pubkey::new_rand();

        assert_eq!(
            Change::new(&system_program_id, &system_program_id)
                .owner(&alice_program_id)
                .verify(),
            Ok(()),
            "system program should be able to change the account owner"
        );
        assert_eq!(
            Change::new(&system_program_id, &system_program_id)
                .owner(&alice_program_id)
                .read_only()
                .verify(),
            Err(InstructionError::ModifiedProgramId),
            "system program should not be able to change the account owner of a read-only account"
        );
        assert_eq!(
            Change::new(&mallory_program_id, &system_program_id)
                .owner(&alice_program_id)
                .verify(),
            Err(InstructionError::ModifiedProgramId),
            "system program should not be able to change the account owner of a non-system account"
        );
        assert_eq!(
            Change::new(&mallory_program_id, &mallory_program_id)
                .owner(&alice_program_id)
                .verify(),
            Ok(()),
            "mallory should be able to change the account owner, if she leaves clear data"
        );
        assert_eq!(
            Change::new(&mallory_program_id, &mallory_program_id)
                .owner(&alice_program_id)
                .data(vec![42], vec![0])
                .verify(),
            Ok(()),
            "mallory should be able to change the account owner, if she leaves clear data"
        );
        assert_eq!(
            Change::new(&mallory_program_id, &mallory_program_id)
                .owner(&alice_program_id)
                .executable(true, true)
                .data(vec![42], vec![0])
                .verify(),
            Err(InstructionError::ModifiedProgramId),
            "mallory should not be able to change the account owner, if the account executable"
        );
        assert_eq!(
            Change::new(&mallory_program_id, &mallory_program_id)
                .owner(&alice_program_id)
                .data(vec![42], vec![42])
                .verify(),
            Err(InstructionError::ModifiedProgramId),
            "mallory should not be able to inject data into the alice program"
        );
    }

    #[test]
    fn test_verify_account_changes_executable() {
        let owner = solana_sdk::pubkey::new_rand();
        let mallory_program_id = solana_sdk::pubkey::new_rand();
        let system_program_id = system_program::id();

        assert_eq!(
            Change::new(&owner, &system_program_id)
                .executable(false, true)
                .verify(),
            Err(InstructionError::ExecutableModified),
            "system program can't change executable if system doesn't own the account"
        );
        assert_eq!(
            Change::new(&owner, &system_program_id)
                .executable(true, true)
                .data(vec![1], vec![2])
                .verify(),
            Err(InstructionError::ExecutableDataModified),
            "system program can't change executable data if system doesn't own the account"
        );
        assert_eq!(
            Change::new(&owner, &owner).executable(false, true).verify(),
            Ok(()),
            "owner should be able to change executable"
        );
        assert_eq!(
            Change::new(&owner, &owner)
                .executable(false, true)
                .read_only()
                .verify(),
            Err(InstructionError::ExecutableModified),
            "owner can't modify executable of read-only accounts"
        );
        assert_eq!(
            Change::new(&owner, &owner).executable(true, false).verify(),
            Err(InstructionError::ExecutableModified),
            "owner program can't reverse executable"
        );
        assert_eq!(
            Change::new(&owner, &mallory_program_id)
                .executable(false, true)
                .verify(),
            Err(InstructionError::ExecutableModified),
            "malicious Mallory should not be able to change the account executable"
        );
        assert_eq!(
            Change::new(&owner, &owner)
                .executable(false, true)
                .data(vec![1], vec![2])
                .verify(),
            Ok(()),
            "account data can change in the same instruction that sets the bit"
        );
        assert_eq!(
            Change::new(&owner, &owner)
                .executable(true, true)
                .data(vec![1], vec![2])
                .verify(),
            Err(InstructionError::ExecutableDataModified),
            "owner should not be able to change an account's data once its marked executable"
        );
        assert_eq!(
            Change::new(&owner, &owner)
                .executable(true, true)
                .lamports(1, 2)
                .verify(),
            Err(InstructionError::ExecutableLamportChange),
            "owner should not be able to add lamports once marked executable"
        );
        assert_eq!(
            Change::new(&owner, &owner)
                .executable(true, true)
                .lamports(1, 2)
                .verify(),
            Err(InstructionError::ExecutableLamportChange),
            "owner should not be able to add lamports once marked executable"
        );
        assert_eq!(
            Change::new(&owner, &owner)
                .executable(true, true)
                .lamports(2, 1)
                .verify(),
            Err(InstructionError::ExecutableLamportChange),
            "owner should not be able to subtract lamports once marked executable"
        );
        let data = vec![1; 100];
        let min_lamports = Rent::default().minimum_balance(data.len());
        assert_eq!(
            Change::new(&owner, &owner)
                .executable(false, true)
                .lamports(0, min_lamports)
                .data(data.clone(), data.clone())
                .verify(),
            Ok(()),
        );
        assert_eq!(
            Change::new(&owner, &owner)
                .executable(false, true)
                .lamports(0, min_lamports - 1)
                .data(data.clone(), data)
                .verify(),
            Err(InstructionError::ExecutableAccountNotRentExempt),
            "owner should not be able to change an account's data once its marked executable"
        );
    }

    #[test]
    fn test_verify_account_changes_data_len() {
        let alice_program_id = solana_sdk::pubkey::new_rand();

        assert_eq!(
            Change::new(&system_program::id(), &system_program::id())
                .data(vec![0], vec![0, 0])
                .verify(),
            Ok(()),
            "system program should be able to change the data len"
        );
        assert_eq!(
            Change::new(&alice_program_id, &system_program::id())
            .data(vec![0], vec![0,0])
            .verify(),
        Err(InstructionError::AccountDataSizeChanged),
        "system program should not be able to change the data length of accounts it does not own"
        );
    }

    #[test]
    fn test_verify_account_changes_data() {
        let alice_program_id = solana_sdk::pubkey::new_rand();
        let mallory_program_id = solana_sdk::pubkey::new_rand();

        assert_eq!(
            Change::new(&alice_program_id, &alice_program_id)
                .data(vec![0], vec![42])
                .verify(),
            Ok(()),
            "alice program should be able to change the data"
        );
        assert_eq!(
            Change::new(&mallory_program_id, &alice_program_id)
                .data(vec![0], vec![42])
                .verify(),
            Err(InstructionError::ExternalAccountDataModified),
            "non-owner mallory should not be able to change the account data"
        );
        assert_eq!(
            Change::new(&alice_program_id, &alice_program_id)
                .data(vec![0], vec![42])
                .read_only()
                .verify(),
            Err(InstructionError::ReadonlyDataModified),
            "alice isn't allowed to touch a CO account"
        );
    }

    #[test]
    fn test_verify_account_changes_rent_epoch() {
        let alice_program_id = solana_sdk::pubkey::new_rand();

        assert_eq!(
            Change::new(&alice_program_id, &system_program::id()).verify(),
            Ok(()),
            "nothing changed!"
        );
        assert_eq!(
            Change::new(&alice_program_id, &system_program::id())
                .rent_epoch(0, 1)
                .verify(),
            Err(InstructionError::RentEpochModified),
            "no one touches rent_epoch"
        );
    }

    #[test]
    fn test_verify_account_changes_deduct_lamports_and_reassign_account() {
        let alice_program_id = solana_sdk::pubkey::new_rand();
        let bob_program_id = solana_sdk::pubkey::new_rand();

        // positive test of this capability
        assert_eq!(
            Change::new(&alice_program_id, &alice_program_id)
            .owner(&bob_program_id)
            .lamports(42, 1)
            .data(vec![42], vec![0])
            .verify(),
        Ok(()),
        "alice should be able to deduct lamports and give the account to bob if the data is zeroed",
    );
    }

    #[test]
    fn test_verify_account_changes_lamports() {
        let alice_program_id = solana_sdk::pubkey::new_rand();

        assert_eq!(
            Change::new(&alice_program_id, &system_program::id())
                .lamports(42, 0)
                .read_only()
                .verify(),
            Err(InstructionError::ExternalAccountLamportSpend),
            "debit should fail, even if system program"
        );
        assert_eq!(
            Change::new(&alice_program_id, &alice_program_id)
                .lamports(42, 0)
                .read_only()
                .verify(),
            Err(InstructionError::ReadonlyLamportChange),
            "debit should fail, even if owning program"
        );
        assert_eq!(
            Change::new(&alice_program_id, &system_program::id())
                .lamports(42, 0)
                .owner(&system_program::id())
                .verify(),
            Err(InstructionError::ModifiedProgramId),
            "system program can't debit the account unless it was the pre.owner"
        );
        assert_eq!(
            Change::new(&system_program::id(), &system_program::id())
                .lamports(42, 0)
                .owner(&alice_program_id)
                .verify(),
            Ok(()),
            "system can spend (and change owner)"
        );
    }

    #[test]
    fn test_verify_account_changes_data_size_changed() {
        let alice_program_id = solana_sdk::pubkey::new_rand();

        assert_eq!(
            Change::new(&alice_program_id, &system_program::id())
                .data(vec![0], vec![0, 0])
                .verify(),
            Err(InstructionError::AccountDataSizeChanged),
            "system program should not be able to change another program's account data size"
        );
        assert_eq!(
            Change::new(&alice_program_id, &alice_program_id)
                .data(vec![0], vec![0, 0])
                .verify(),
            Err(InstructionError::AccountDataSizeChanged),
            "non-system programs cannot change their data size"
        );
        assert_eq!(
            Change::new(&system_program::id(), &system_program::id())
                .data(vec![0], vec![0, 0])
                .verify(),
            Ok(()),
            "system program should be able to change account data size"
        );
    }

    #[test]
    fn test_verify_account_changes_owner_executable() {
        let alice_program_id = solana_sdk::pubkey::new_rand();
        let bob_program_id = solana_sdk::pubkey::new_rand();

        assert_eq!(
            Change::new(&alice_program_id, &alice_program_id)
                .owner(&bob_program_id)
                .executable(false, true)
                .verify(),
            Err(InstructionError::ExecutableModified),
            "Program should not be able to change owner and executable at the same time"
        );
    }

    #[test]
    fn test_debug() {
        let mut instruction_processor = InstructionProcessor::default();
        #[allow(clippy::unnecessary_wraps)]
        fn mock_process_instruction(
            _program_id: &Pubkey,
            _data: &[u8],
            _invoke_context: &mut dyn InvokeContext,
        ) -> Result<(), InstructionError> {
            Ok(())
        }
        #[allow(clippy::unnecessary_wraps)]
        fn mock_ix_processor(
            _pubkey: &Pubkey,
            _data: &[u8],
            _context: &mut dyn InvokeContext,
        ) -> Result<(), InstructionError> {
            Ok(())
        }
        let program_id = solana_sdk::pubkey::new_rand();
        instruction_processor.add_program(program_id, mock_process_instruction);
        instruction_processor.add_program(program_id, mock_ix_processor);

        assert!(!format!("{:?}", instruction_processor).is_empty());
    }
}
